The present invention relates to a coaxial dielectric resonator (referred to as dielectric S.I.R. (Stepped Impedance Resonator) hereinafter) which is used at high frequency.
FIG. 9 shows a typical conventional dielectric S.I.R. This dielectric S.I.R. is composed of a cylindrical outer conductor 1, an inner conductor 2 and a dielectric member 3. The outside diameter of the outer conductor 1 is reduced at the open end of the outer conductor 1 over a predetermined axial length as compared with the closed end of the outer conductor 1 so as to reduce impedance. Another known dielectric S.I.R. is shown in FIG. 10. Both these known dielectric S.I.R.s have cylindrical configurations.
In these known dielectric S.I.R.s, a large reduction of the Q value in the resonance circuit is inevitable, which makes it difficult to reduce the size of the filter in the resonator.
Another problem encountered with the known dielectric S.I.R.s is that the space factor is reduced due to the fact that the filter has to be placed in a case which has a cylindrical configuration.